1. Field of the Invention
The present invention relates to a thermal contact-bonding apparatus such as a vacuum press, a vacuum hot press, or a double vacuum apparatus. The present invention more specifically relates to a method and an apparatus for thermally contact-bonding a surface of a material to be processed which is brought into contact with a resin sheet in a clean state.
2. Related Background Art
A thermal contact-bonding apparatus such as a vacuum press, a vacuum hot press, or a double vacuum apparatus is suitably used for laminate molding of an outer surface of a molded substrate having a three-dimensional shape including a cabinet for audio or visual equipment, furniture, and a container by bonding a decorative sheet such as a transfer sheet or an adhesive sheet along the outer surface of such a molded substrate, for example, for surface finishing such as decoration.
For example, as a method of bonding and laminating a decorative sheet on an outer surface of a molded substrate, a method disclosed by Japanese Patent Publication No. S56-045768 or the like is known which includes dividing an upper chamber and a lower chamber with a decorative sheet; pressing the upper chamber while reducing a pressure of the lower chamber provided with a molded substrate by vacuum sucking to cause a pressure difference between the chambers, and heating and softening the decorative sheet substantially at the same time to bond the decorative sheet along an outer surface of the molded substrate. The lamination method assumes that the decorative sheet be generally an adhesive sheet, but the lamination method can also be employed in a case where the decorative sheet is a transfer sheet. In this case, a transfer portion is bonded, and then a release substrate sheet alone is peeled off while the transfer portion remains.
The above-mentioned thermal contact-bonding method involves pressing a decorative sheet against a molded substrate by a pressure difference alone. Thus, pressing force of the decorative sheet against the molded substrate may be insufficient or may be partially uneven. A decorative sheet cannot be completely adhered to uneven portions or curving portions of a molded substrate having a large height difference in uneven portions provided on an outer surface or having a large curvature at edge portions or localized portions of the outer surface. Thus, bonding failure easily occurs.
A thermal contact-bonding method is proposed to solve such problems mentioned above. A method disclosed in Japanese Patent Application Laid-Open No. S57-105310 or the like involves, for example, heating an elastic cover member of silicone rubber or the like with radiation heat to a predetermined temperature by providing a heater in a sheet-side chamber and heating the sheet-inside chamber; lowering the sheet-side chamber toward a suction holder having a work and a sheet placed thereon; while sucking the elastic cover member and the sheet under vacuum along a curve shape of the work, pressurizing the inside of the sheet-side chamber to bring the elastic cover member into contact with the sheet and pressurizing the both.
There has been proposed methods employing such a thermal contact-bonding method such as a method of bonding a decorative sheet of a synthetic resin having a pattern or the like printed thereon to an outer surface of wood, metal, or the like; a method of producing a curving multilayer wiring board used for antennas, mobile communication, or the like; and a method of producing an IC lead frame having a composite structure of a conductive metal sheet and an insulating material sheet laminated on each other.
Further, Japanese Patent Application Laid-Open Nos. H07-335921 and H08-306946 discloses a method of forming an electrode for a photovoltaic device such as a solar cell by using a thermal contact-bonding method.
A typical structure of the photovoltaic device includes: a semiconductor layer having a p-n junction; a light receiving surface electrode of a transparent conductive oxide formed on a light receiving surface of the semiconductor layer; a collecting electrode consisting of a relatively thin metal for collecting a current on the light receiving surface electrode; and an electrode consisting of a relatively thick metal called “busbar” for collecting the current collected at the collecting electrode.
An electrode structure of the photovoltaic device as disclosed in, for example, U.S. Pat. No. 4,260,429 has been proposed, and this structure includes an electrode consisting of a metal wire coated with a polymer containing conductive particles, for example. An invention described in U.S. Pat. No. 4,260,429 allows a small electrical resistance loss even when a metal wire having good conductivity such as copper is used to form a long collecting electrode, and an aspect ratio of 1:1, whereby a shadow loss can also be reduced. A wire can be fixed by bonding through a simple thermal contact-bonding method using a conductive adhesive.
A specific example of a method of forming an electrode for a photovoltaic device will be described with reference to FIGS. 5A to 5B and 6A to 6I. FIGS. 5A to 5B are schematic diagrams each showing a structure of a photovoltaic device, which is a material to be processed. FIG. 5A is a schematic diagram of the photovoltaic device seen from a light-receiving surface side, and FIG. 5B is a schematic diagram of the photovoltaic device seen from a non-light-receiving surface side.
In FIGS. 5A and 5B, a photovoltaic device 504 (200 mm×200 mm) includes a substrate, a lower electrode layer, amorphous silicon having a photovoltaic function, and an upper electrode layer. A serial number 514 of the photovoltaic device 504 is printed in an area of 10 mm×30 mm, which is a part of a non-light-receiving surface of the photovoltaic device 504, with a continuous ink jet printer.
The photovoltaic device 504 includes: a stainless sheet having a thickness of 150 μm for supporting the entire photovoltaic device 504; and a lower electrode layer directly on the substrate formed by sequentially depositing Al and ZnO each to a thickness of several thousands Å by a sputtering process. Amorphous silicon is formed by sequentially depositing respective layers of n-type, i-type, p-type, n-type, i-type, and p-type by a plasma CVD process. The layers each have a thickness of about 150, 4,000, 100, 100, 800, and 100 Å, respectively. The upper electrode layer consists of a transparent electrode film which is an indium oxide thin film having a thickness of about 700 Å formed by depositing In in an O2 atmosphere by a resistance heating process.
In order to prevent an adverse effect of a short circuit between the substrate and the transparent electrode film occurring at the time of cutting a periphery of the photovoltaic device on an effective light-receiving area, an etching paste containing FeCl3, AlCl3, or the like is applied to the transparent electrode film by a screen printing process, heated, and washed. Thus, a part of the transparent electrode member of the photovoltaic device 504 is linearly removed to form an etching line 511.
Then, a copper foil strip (length: 200 mm, width: 5 mm, thickness: 100 μm), which is a back surface side conductive foil member 512, is formed on two edge portions of the non-light receiving surface side of the photovoltaic device 504 by a method disclosed in Japanese Patent Application Laid-Open No. H08-139349.
An insulating two-sided adhesive tape (not shown) having a polyimide base member (length: 200 mm, width: 5 mm, thickness: 50 μm) is applied on two edge portions of the light-receiving surface side of the photovoltaic device 504, two edge portions facing the back surface side conductive foil member. A conductive adhesive-applied metal wire 505 prepared in advance by applying a conductive adhesive consisting of a carbon paste on a copper wire of Φ 100 μm is continuously formed on the photovoltaic device 504 and the insulating two-sided adhesive tape at a pitch of 20 mm, to thereby form a collecting electrode. Further, a conductive foil member 513, which is an electrode for collecting the collecting electrodes, is formed on the insulating two-sided adhesive tape. To be specific, a copper foil strip (length: 200 mm, width: 5 mm, thickness: 100 μm) is arranged on the insulating two-sided adhesive tape, and the whole is subjected to heat and pressure fixing under the conditions of 200° C., 0.098 MPa, and 120 seconds.
FIGS. 6A to 6I are sectional schematic diagrams each showing a thermal contact-bonding apparatus for realizing the above-mentioned heat and pressure fixing. In FIGS. 6A to 6I, reference numeral 601 denotes an upper chamber; 602, a resin sheet; 603, a hot plate provided with a heater inside and on which a material to be processed is placed; and 608, a lower chamber.
The thermal contact-bonding apparatus stands by at the state that the upper chamber 601 is lowered, and the upper chamber 601, the lower chamber 608, and the resin sheet 602 are heated by the hot plate 603 (FIG. 6A).
Next, the upper chamber 601 is raised in order to carry a photovoltaic device, which is a material to be processed, onto the hot plate. The photovoltaic device, which is a material to be processed, is carried and placed on the hot plate 603 with its collecting-electrode-formed surface facing upward (FIGS. 6B and 6C).
Then, the inside of the upper chamber 601 is vacuum evacuated. The upper chamber 601 is lowered. Then, the inside of the lower chamber 608 is vacuum evacuated, to thereby attach the resin sheet 602 uniformly to a surface of the material to be processed (FIGS. 6D, 6E, and 6F).
Then, the upper chamber 601 is opened to the atmosphere. The resin sheet 602 is pressed against the material to be processed at a pressure of 0.098 MPa by the atmospheric pressure while the temperature of the whole is controlled to 200° C. with the hot plate 603 to carry out a thermal contact-bonding press for 120 seconds (FIG. 6G).
After the thermal contact-bonding press, the lower chamber 608 is opened to the atmosphere. The upper chamber 601 is then raised, and the processed material is carried out (FIGS. 6H and 6I).
After the processed material is carried out, the upper chamber 601 is then lowered and heated as shown in FIG. 6A to prevent decrease in temperatures of the upper chamber 601 and the lower chamber 608. Timings of carrying the material to be processed into and the processed material out of the thermal contact-bonding apparatus may be changed depending on pre- and post-processings taken in the thermal contact-bonding apparatus. A time period for raising the upper chamber and opening the thermal contact-bonding apparatus may also be changed in order to carrying the material to be processed into and the processed material out of the thermal contact-bonding apparatus. The temperatures of the upper and lower chambers, the resin sheet, or the like decrease during opening of the thermal contact-bonding apparatus. The upper chamber is desirably lowered when the thermal contact-bonding apparatus stands by, that is, when the material to be processed is not carried into the thermal contact-bonding apparatus, to thereby maintain a constant ambient temperature for continuous, stable thermal contact-bonding.
The above-mentioned thermal contact-bonding method involves a method of fixing a collecting electrode to a photovoltaic device by heat or pressure. Increasing the number of processing cycles of the thermal contact-bonding apparatus causes adhering of a serial number print paint or the like on the back surface of the photovoltaic device to the surface of the heating plate, adhering of the paint again from the hot plate to the resin sheet in the stand-by state of the thermal contact-bonding apparatus; and adhering of the paint adhered to the resin sheet again to the light-receiving surface of the photovoltaic device in the next thermal contact-bonding processing, thereby resulting in problems that the light-receiving surface is contaminated, and that characteristics of the photovoltaic device deteriorate significantly.